Sound-Absorbing Lining for Motor Vehicles, Particularly Engine Hood Lining

ABSTRACT

The invention relates to a self-supporting, sound-absorbing lining for the engine bonnet of motor vehicles, comprising at least one layer of open-cell foamed material which on at least one side is covered with a covering nonwoven, an open-pored coating that connects the covering nonwoven to the layer of foamed material being applied to at least one side of the layer of foamed material. In order to improve this type of lining with regard to its dimensional stability at temperatures of up to 180° C. and when in a damp environment and without using nonwovens made from synthetic mineral fibres, the invention proposes that the coating be formed from a powder mixture that consists of at least one thermoplastic component, at least one cross-linking component and mineral microbodies, preferably hollow microbodies.

The invention relates to a self-supporting lining that absorbs airborne sound, particularly in the form of a face wall lining for the engine hood or on the engine side, having at least one layer of open-cell foam material, which layer is laminated at least on one side to a non-woven fabric cover, whereby an open-pore coating that connects the non-woven fabric cover with the foam material layer is disposed at least on one side of the foam material layer.

Such linings are known, for example, from DE 85 27 746 U1. The sound-absorbing panel described there consists of a foam material layer of polyurethane resin foam, phenolic resin foam, or melamine resin foam, which is laminated on both sides to thin cover layers. The cover layers consist, in particular, of mineral fiber or glass fiber non-woven fabrics. They are supposed to protect the foam material layer, which can easily be damaged mechanically, from damage, and to absorb the tensile and shear forces that occur in the sandwich structure, because of its inherent weight and under stress on the sound-absorbing panel, and thereby to bring about sufficient rigidity and inherent carrying strength of the sound-absorbing panel. In this connection, lamination of the non-woven fabric cover onto the foam material layer usually takes place by means of application of a spray adhesive, by means of binders that are water soluble or contain solvents, or also by means of introduction of a plastic film that melts under the effect of heat and connects the layers when it hardens again.

The use of mineral fiber or glass fiber non-woven fabrics is problematic, particularly in the production of such sound-absorbing parts, since contact with artificial mineral fibers can cause skin irritations among the persons employed in production. Furthermore, microscopically small fibers are released from artificial mineral fibers, particularly when cutting non-woven cover fabrics to size, and these possess carcinogenic properties.

Furthermore, there is the problem that conventional sound-absorbing parts of the type known from DE 85 27 746 U1 demonstrate shrinkage and bending values that are often impermissible, at high temperatures and humidity, in the engine compartment of motor vehicles.

The present invention is therefore based on the task of making available a lining of the type stated initially, which can be produced free of mineral fibers, but nevertheless demonstrates improved shape stability at temperatures in the minus degree range as well as at high temperatures up to +180° C., particularly also in a humid environment.

This task is accomplished, according to the invention, by means of a lining having the characteristics of claim 1.

The sound-absorbing lining according to the invention has at least one open-cell foam material layer that is laminated at least on one side to a non-woven fabric cover, whereby an open-pore coating that connects the non-woven fabric cover with the foam material layer is applied at least on one side of the foam material layer; this coating is formed from a powder mixture that is composed of at least one thermoplastic component, at least one cross-linking component, and mineral micro-bodies.

The lining according to the invention is particularly suitable as a sound-absorbing part in the engine compartment of a motor vehicle. It is characterized by excellent shape stability at temperatures up to approximately 180° C., in the alternating climate test, whereby it is possible to do without the use of mineral fibers and glass fibers in their production. Also, the water absorption of the lining according to the invention is significantly reduced as compared with conventional sound-absorbing parts of this type. The lining according to the invention can be heat-shaped or hot-pressed in excellent manner during its production, so that even difficult geometries with small radii of curvature can be implemented.

The foam material layer of the lining according to the invention is preferably formed from duroplastic foam material, particularly preferably from melamine resin foam material. Melamine foam resin demonstrates excellent temperature resistance and is considered to be very flame-resistant.

The non-woven fabric cover or non-woven fabric covers of the lining according to the invention are preferably formed from polyester fibers. Polyester fiber non-woven fabric has a high temperature resistance and is furthermore resistant to rotting.

It was found by the inventors that the temperature stability and shape stability of the lining according to the invention is particularly good if the open-pore coating that connects the non-woven fabric cover with the foam material layer is composed of 15 to 45 wt.-% thermoplastic plastic, 8 to 25 wt.-% duroplastic binder, and 50 to 70 wt.-% mineral micro-bodies.

The thermoplastic component or components of the coating preferably consist of plastic or plastics from the group of polyolefins, copolyesters, or copolyamides. It is advantageous, in particular, to use mixtures of these thermoplastic plastics in the coating.

The cross-linking component of the coating, on the other hand, is preferably formed from phenolic resin, melamine resin and/or epoxy resin. Very good shape stability was achieved, in particular, when the coating contains 2 to 6 wt.-% phenolic resin binder and 8 to 15 wt.-% melamine resin binder.

The mineral micro-bodies of the coating are preferably formed from hollow mineral micro-bodies. This not only has an advantageous effect with regard to a low weight per surface area of the coating, but also improves the sound absorption of the lining according to the invention.

The open-pore coating can be applied on one side, or preferably on both sides of the foam material layer. According to an advantageous embodiment of the lining according to the invention, the coating can also be applied between two or more thin foam material layers. In this way, the shape stability of the lining can be further improved.

In terms of process technology, the coating can be applied as a powder mixture, at first, onto the foam material layer, or, alternatively, also onto the side of the non-woven fabric cover that faces the foam material layer. After the thermal lamination process has been concluded, the coating connects the non-woven fabric cover, in each instance, with the foam material layer.

Another advantageous embodiment of the lining according to the invention is characterized in that the foam material layer and/or the non-woven fabric cover/non-woven fabric covers are made to be hydrophobic and/or oleophobic. In this way, the liquid absorption of the lining can be minimized, to a great extent.

Other preferred and advantageous embodiments of the sound-absorbing part according to the invention are indicated in the dependent claims.

In the following, the invention will be explained in greater detail using a drawing that represents several exemplary embodiments. This shows:

FIG. 1 a schematic cross-sectional view of a lining according to the invention, in a first exemplary embodiment;

FIG. 2 a schematic cross-sectional view of a lining according to the invention, in a second exemplary embodiment;

FIG. 3 a schematic cross-sectional view of a lining according to the invention, in a third exemplary embodiment; and

FIG. 4 a schematic representation of a system for the production of a lining according to the invention.

The linings 1, 1′, 1″ shown in the drawing are sound-absorbing lining parts for the engine compartment of a motor vehicle, e.g. engine hood linings or face wall linings that absorb airborne sound.

The linings 1, 1′ shown in FIGS. 1 and 2 are formed from an open-cell foam material layer 2, in each instance, which is laminated to an air-permeable non-woven fabric cover 3, 4 on both sides. The foam material layer 2 has an average thickness in the range of approximately 8 to 30 mm, and preferably consists of duroplastic foam material. The foam material layer is relatively light; its volumetric weight in the unpressed state lies in the range of about 7 to 12 kg/m³. Particularly preferably, it consists of melamine resin foam, particularly of a melamine resin foam that has been adjusted to be hydrophobic and/or oleophobic.

The non-woven fabric covers 3, 4 are formed from polyester fibers or from mixtures containing polyester fibers. In this connection, these can be, in particular, needled non-woven fabrics, spun-bonded non-woven fabrics, polyester non-woven fabrics bonded with acrylate binder, for example, and/or mixed-fiber non-woven fabrics, such as polyester/viscose non-woven fabrics. The weight per surface area of the non-woven fabric cover 3, 4, in each instance, lies in the range of approximately 30 to 160 g/m². The non-woven fabric covers 3, 4 can made to be hydrophobic and/or oleophobic.

In FIG. 1, a coating 5 that connects the non-woven fabric cover 3 with the foam material layer 2 is disposed on one side of the foam material layer 2. The coating 5 is formed from a powder mixture that is composed of at least one thermoplastic component, at least one cross-linking component, and mineral (inorganic) micro-bodies.

The thermoplastic component is, for example, polyethylene, particularly high-density polyethylene (HD-PE). However, the use of polyethylene or HDPE is not compulsory. Likewise, another plastic from the group of polyolefins, copolyesters, or copolyamides can be used in the powder mixture as the thermoplastic component. The MFI value (MFI=Melt Flow Index, Melt Index), i.e. the viscosity of the plastic used as the thermoplastic component should be selected to be as low as possible. Preferably, the MFI value of the thermoplastic component of the powder mixture lies in the range of about 18 to 22 g/10 min (190°/2.16 kg), particularly in the range of 18 to 20 g/10 min (190°/2.16 kg).

The cross-linking component of the coating 5 is formed, for example, from phenolic resin, phenolic formaldehyde resin, melamine resin, melamine formaldehyde resin, melamine phenolic resin, and/or epoxy resin.

The mineral micro-bodies of the coating 5 preferably consist essentially of hollow mineral micro-bodies. The grain size of the micro-bodies lies in the range of 0 to 400 μm, preferably in the range of 0 to 300 μm.

The powder mixture on which the open-pore coating 5 is based is preferably composed of 20 to 30 wt.-% thermoplastic plastic, 10 to 20 wt.-% duroplastic binder, and 55 to 65 wt.-% mineral micro-bodies, whereby the duroplastic binder can also comprise several components.

A suitable powder mixture could, for example, have the following composition:

-   -   25.0 wt.-% polyolefin polymer powder, e.g. HDPE, having a grain         size up to 200 μm,     -   4.0 wt.-% phenolic resin,     -   11.0 wt.-% melamine resin, and     -   60.0 wt.-% hollow mineral micro-bodies.

The melting range of such a powder mixture lies approximately in the range of 100 to 130° C.

The lining part 1′ shown in FIG. 2 differs from the exemplary embodiment according to FIG. 1 essentially only in that the coating 5 is applied or disposed on both sides of the foam material layer 2. The coating 5, 5.1, 5.2 has a weight per surface area, in each instance, in the range of 50 to 200 g/m². Both lining parts 1, 1′ are free of artificial mineral fibers.

FIG. 3 shows another exemplary embodiment of the lining according to the invention. Here, the lining 1″ is formed from two relatively thin open-cell foam material layers 2.1 and 2.2. The foam material layers 2.1, 2.1 are laminated to an air-permeable non-woven fabric cover 3, 4, in each instance. The foam material layers 2.1, 2.2 and the non-woven fabric covers 3, 4 correspond, with regard to their material, to the exemplary embodiment according to FIG. 1. The non-woven fabric covers 3, 4 are connected with the related foam material layer 2.1 or 2.2 by way of a coating 5.1, 5.2, in each instance, which corresponds to the coating 5 of the exemplary embodiment according to FIG. 1. In FIG. 3, it can be seen that a corresponding coating 5.3 is also applied between the foam material layers 2.1 and 2.2.

FIG. 4 schematically shows a system for the production of a sound-absorbing lining part 1, 1′ according to the invention.

A web 9 of open-cell, duroplastic foam material and an upper web 10 as well as a lower web 11 of a non-woven fabric as the non-woven fabric cover are unwound from supply rollers 6, 7, 8. The duroplastic foam material that is used can be impregnated with a heat-hardening, not yet cross-linked binder such as melamine resin or phenolic resin, for example.

The foam material web 9 and the lower non-woven fabric web 11 each have a sprinkler head 12, 13 or the like for applying the powder mixture indicated above assigned to them. At least one heating device (e.g. a heat radiator) 14, 15 for starting to melt or melting the powder mixture is disposed downstream from the sprinkler heads 12, 13.

The webs 9, 10, 11 are brought together and pressed against one another by means of a roller gap of adjacent contact pressure rollers 16, 17. The foam material web 9, laminated to non-woven fabric covers 10, 11 in this manner, is subsequently passed to a heated shape-pressing die 18, which comprises an upper die 19 and a lower die 20, which can be moved towards and away from one another in accordance with the double arrow 21. A cutting device 22.1, 22.2 for producing suitable cutouts 23 precedes the shape-pressing die 18. Alternatively or supplementally, the shape-pressing die 18 itself can also be provided with a cutting device. The cut-out 23, in each instance, of the foam material web 9 laminated to the non-woven fabric covers 10, 11, is permanently deformed in the heated shape-pressing die 18, in accordance with the desired contour of the required lining part 1, 1′, whereby the edge of the shaped part, in each instance, is pressed (embossed) so strongly that the foam material layer 2 is finally compacted into a compact circumferential edge strip 24 (cf. FIGS. 1 and 2). 

1. Self-supporting lining (1, 1′, 1″) that absorbs airborne sound, for motor vehicles, particularly in the form of an engine hood lining or engine-side face wall lining, having at least one open-cell foam material layer (2; 2.1, 2.2) that is laminated to a non-woven fabric cover (3, 4) on at least one side, whereby an open-pore coating (5) that connects the non-woven fabric cover with the foam material is applied on at least one side of the foam material layer, wherein the coating (5) is formed from a powder mixture that is composed of at least one thermoplastic component, at least one cross-linking component, and mineral micro-bodies.
 2. Lining according to claim 1, wherein at least two foam material layers (2.1, 2.2) are present, wherein the coating (5.3) is also applied between at least two of the foam material layers (2.1, 2.2).
 3. Lining according to claim 1, wherein the foam material layer (2) or foam material layers (2.1, 2.2) are formed from duroplastic foam material.
 4. Lining according to claim 1, wherein it is laminated to a non-woven fabric cover (3, 4) on both sides.
 5. Lining according to claim 1, wherein the coating (5.1, 5.2) is applied to both sides of the foam material layer (2).
 6. Lining according to claim 1, wherein the non-woven fabric cover (3) or the non-woven fabric covers (3, 4) are formed from polyester fibers or mixtures containing polyester fibers.
 7. Lining according to claim 1, wherein the coating (5; 5.1, 5.2, 5.3) is composed of 15-45 wt.-% thermoplastic plastic, 8-25 wt.-% duroplastic binder, and 50-70 wt.-% mineral micro-bodies.
 8. Lining according to claim 1, wherein the coating (5; 5.1, 5.2, 5.3) is composed of 20-30 wt.-% thermoplastic plastic, 10-20 wt.-% duroplastic binder, and 55-65 wt.-% mineral micro-bodies.
 9. Lining according to claim 1, wherein the mineral micro-bodies are formed from hollow mineral micro-bodies.
 10. Lining according to claim 1, wherein the thermoplastic component of the coating (5; 5.1, 5.2, 5.3) is a plastic from the group of polyolefins, copolyesters, or copolyamides.
 11. Lining according to claim 1, wherein the cross-linking component of the coating (5; 5.1, 5.2, 5.3) is formed from phenolic resin, melamine resin, melamine/phenolic resin, and/or epoxy resin.
 12. Lining according to claim 1, wherein the coating (5) contains 2-6 wt.-% phenolic resin binder and 8-15 wt.-% melamine resin binder.
 13. Lining according to claim 1, wherein the coating (5, 5.1, 5.2, 5.3) is applied to the foam material layer (2) or the non-woven fabric cover (3, 4) with a weight per surface area in the range of 50 to 200 g/m².
 14. Lining according to claim 1, wherein the micro-bodies have a grain size less than/equal to 400 μm, preferably less than/equal to 300 μm.
 15. Lining according to claim 1, wherein it is free of mineral fibers, particularly free of glass fibers.
 16. Lining according to claim 1, wherein the foam material layer (2; 2.1, 2.2) and/or the non-woven fabric cover (3)/the non-woven fabric covers (3, 4) are made to be hydrophobic and/or oleophobic. 